Examples of electronic components that require an airtight seal include crystal resonators, crystal filters, crystal oscillators, and other such piezoelectric resonator devices. With all of these products, a metal thin-film electrode is formed on the surface of a crystal plate (piezoelectric resonator element), and an airtight seal is provided to protect this metal thin-film electrode from the outside atmosphere.
Because of the need for the surface mounting of components, these piezoelectric resonator devices are increasingly being housed hermetically inside a package composed of a ceramic material. For instance, Patent Document 1 discloses a package comprising a base (substrate) wit a concave cross section having four electrode pads (connecting electrodes) for the mounting of a crystal plate on the front and back faces on which are formed drive electrodes, and a cap (lid) with an inverted concave cross section, wherein this package is composed of a ceramic material and these components are hermetically sealed. Here, of the four electrode pads, two electrode pads that are opposite to each other in the long-side direction are connected to each other and given the same potential by connecting electrodes (metal wiring), so that two pairs of electrode pads are disposed in linear symmetry around the base center, so when a crystal plate is electromechanically joined to the pairs of electrode pads by a conductive joining material, the assembly can be carried out without worrying about directionality in mounting, and this makes the work easier. Also, with the package configuration disclosed in Patent Document 1, it is possible either for the crystal plate to be supported at just one end in the long-side direction, or for it to be supported at both ends in the long-side direction, which gives this configuration wider applicability.    Patent Document 1: Japanese Laid-Open Patent Application H7-235854